Why No Algorithm Prices a Weldment From a Model
Instant quoting transformed CNC machining and sheet metal. Upload a model, get a price, order. It works because almost everything those processes cost is readable from the geometry: material volume, feature accessibility, tool reach, number of setups, bend count.
Weldments break the model, and it is worth understanding why rather than assuming the platforms are lazy.
What a model does not contain
A STEP file of a welded frame shows you the shape of the finished structure. It does not show:
Weld size. A model shows two plates meeting. It does not say whether that joint is a 5 mm fillet or a prepared full penetration weld, and the difference is several times the weld metal and the shrinkage.
Weld quality level. ISO 5817 level B or level D on the same joint are very different amounts of work, and neither is visible in geometry.
Inspection scope. Whether a weld gets a visual check or full ultrasonic testing changes the price and the schedule. Nothing in the model implies it.
Which faces are machined. A model of the finished part cannot distinguish a face that was cut from one that came off the plate that way, unless somebody says so.
Stress relief. Whether the part goes through an oven between welding and machining is a process decision driven by weld volume, restraint and tolerance. It is not a geometric property.
Material grade nuances. The model may carry a material name. It does not carry the J2 impact requirement, or the L in 316L, or the plate maker heat input limits on abrasion resistant plate.
Every one of those lives in drawing notes, and every one of them moves the price more than the shape does.
The setup problem
There is a second, harder problem. On a heavy weldment the dominant cost is often not cutting but handling: how many times a two tonne part has to be lifted, re-fixtured and re-indicated.
That depends on the machine the shop owns. A frame with bores on four faces is one setup on a horizontal boring mill with a rotary table and four setups on a bed mill. Same model, same drawing, genuinely different cost.
A pricing engine would need to know which machine the part is going on before it could answer, which means the answer is shop specific rather than part specific. That is the opposite of how instant quoting works.
What the platforms actually do
The honest ones treat weldments as a manual quote path, or return an indicative number and then a human reviews it. Where a fully automatic number does appear, it is built on defaults: a default weld size, a default acceptance level, no non-destructive testing, no stress relief, one setup.
On a simple welded bracket those defaults are roughly right and the number is useful. On anything with a tolerance that has to survive machining, the defaults are exactly the assumptions that make a weldment expensive when they turn out to be wrong.
What this means for your RFQ
Two practical consequences.
Send a drawing, not just a model. The drawing carries the weld symbols, the quality level, the inspection scope and the machined features. Without it a shop quotes conservatively, because it is pricing the risk that you meant the expensive version. The RFQ checklist covers the full package.
Expect quotes to vary, and interrogate why. When two competent shops come back far apart on a weldment, the machining plan is usually the reason. Ask how many setups each is planning. The answer explains the price and tells you which quote is carrying the tolerance risk.
Why we work the way we do
This is also why this site is a matching service with a human reading the drawing rather than a quoting engine. We read the part, work out what it actually needs, and pass it to shops whose machines and crane can take it.
That is a slower model than an instant price. On this part type it is the only one that produces a number anyone can stand behind.
Send the drawing and we will tell you what the part needs before it goes to any shop.
Frequently asked questions
Can any platform instant quote a weldment?
Some will return a number for simple weldments from a model. The number is a starting estimate that assumes a default weld size, a default quality level and no inspection. On a simple bracket that is close enough. On a machine base with bore alignment it is not.
Why does CNC machining instant quote so well?
Because almost everything the price depends on is in the model geometry: volume removed, feature accessibility, tool reach, setups. A pricing engine can read those. Weldment cost lives in the drawing notes instead.
So do I need a drawing for every weldment enquiry?
For anything with a tolerance on it, yes. A model tells the shop the shape. The drawing tells it the weld sizes, the quality level, the inspection scope and which features are machined, and those are what the price is made of.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that weld and machine it in house, and we reply within 24 business hours.
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